Method of making ductile iron chromium aluminum alloys



Arm W I 'v. E. BROWNIE I EWSQU METHOD OF MAKING DUC'IILE IRON CHROMIUI'JALUMINUM ALL 0Y5 Filed Dec. 19, 1927 7 an aluminum content .The l atentepr.a l

WERE B. BROWNE, 0F BRACJENRTJDGE, PENNSYLVANIA METHUD Gilli MING-DUC'JEILJE IRQN CHROIVIJEUIWE ALUMINUM ALLOYS application filed December19, 192?. Serial Neat-1,20%.

This invention relates to ferrous alloys and more particularly to alloysin which the principal elements aside from the iron are chromium andaluminum.

any alloys containing iron, chromium and aluminum have from time to timebeen discussed in the technical literature and many such alloys aredisclosed in patents. Many of these alloys show high electricalresistance and also high resistance to oxidation at elevatedtemperatures but as heretofore forged or otherwise worked, they havebeen practically valueless when ductility was necessary. These desirableinherent characteristics have caused much experimental work to be doneby different researchers in an attempt to discover or provide a methodof rendering the alloys ductile and readily workable. r

The experimental work has covered a large number of alloys of this groupand includes those having a chromium range of from 5% to 30% and analuminum range of from 3% to 10%. r

All alloys of this group having' a chromium content ranging from 5% to30% and ranging from 3% to 10%, when forged (which includes rolling) orotherwise worked under ordinary commercial methods develop an extremelylarge grain structure and this large grain structure cannot betransformed into a small grain structure by any known method ofannealing.

arge grain structure renders the finished product, that is, productsmade from these alloys so brittle, that their use in. commercial workhas been exceedingly limited and as a matter of fact where ductility hasbeen necessary, it has been practically impossible to utilize them.

An object of this invention is to provide amethod by means of which thebrittle condition which has heretofore existed in alloys of this typecan be avoided or'overcome and whereby it is possible commercially toprotime such alloys which are readily workable and from which may beproduced .articles such as wire, light gauge sheets,strips, etc., whichare also relatively soft and ductile.

A further and more limited object of this invention is to of whichrelatively soft, ductile resistor grids may be made from ferrous alloyscontaining from 5% to of chromium and from 3% to 10% of aluminum, and inthe drawings, l[ have shown in perspective view one of such grids.

I have discovered that these alloys develop an excessively large grainstructure when eated to a temperature above 1500 F ,and so far as l[know, this large grain structure cannot be transformed into a smallgrain structure by any known method of annealing; lt have found,however, can be so worked as to render them relatively soft and ductile.llhis working in a broad Way consists 'in forging at temperatures below1500 F. and the best results can be obtained by carrying on the finalreduction with the alloy in a relatively cold state and then byannealing the forged material below 1500 F.

I have. carried ,on a large number of experiments' with alloys having achromium range of from 5% to 30% and an aluminum range of from 3% to10%. T find that the alloy best suited (taking all things intoconsideration) for articles such as electrical resistance elements andarticles that are to be subjected to elevated temperatures and mustresist oxidation, is an alloy containing about 12% chromium and about 5%aluminum with the principal part of the remainder 7 iron. The carbonshould be-kept low as possible and is preferably not over 12%.

These alloys are preferably manufactured in an electric arc furnace andthe aluminum is preferably added just before teeming but if desired, maybe added to the ladle;

In carrying out my method an ingot containing the desired percentages ofiron, chromium and aluminum'is heated to a tempera ture just high enough(p to permit it to be cogged or broken down into a bloom withoutrupturing its surface. The temperature which I have found satisfactoryfor this step is about Q OO lF.

After the ingot is cogged or broken down, the bloom is reheated toapproximately 1800 provide a method by means that these alloys F. and sorolled that the finishing passes take place at a temperature well below1500 F.

Beginning at a stage in which the section is considerably larger thanthe finished section desired, all subsequent reductions are made attemperatures not exceeding 1500 F. Finishing is carried out below 1400F. The

final reduction is preferably made cold and I find that the best resultsare obtained when this is about 25%.

In a typical case involving my invention, I started with an ingot twelveinches square and weighing approximately twenty five hun- (lredpounds.The analysis of this ingot was about 12% chromium, about aluminum withthe principal part of the remainder iron.

The ingot was heated to a temperature of about 2000 Fahrenheit androlled to a billet about 5% inches square. The billet was reheated to atemperature of about 1800 F. and rolled down to about 1% inches square.This square section was reheated to 17 00 F. and rolled to a strip about2 inches wide by .072 inches thick and finished ata temperature of about1400 F. The hot rolled strip .072 inches in thickness was then coldrolled to .040 inches in thickness and annealed at a temperature notexceeding 1450 F.

The material produced in this manner had a fine grain structure and wasquite soft and ductile and readily workable.

It will be noted that each step of the forgdecreasing finishingtemperatures, making a final material reduction at a temperature e low1400 F., and then annealing at about 1400 F.

3. The method of making a ductile article from an iron chromium aluminumalloy having a chromium content of about 1020%, an aluminum content ofabout 3-10% with the remainder principally iron, which consists incasting an ingot of such alloys, heating the ingot to about 2000 F.,reducing the same materially to a billet, reheating the billet to about1800 F, reducing the so heated billet materially, reheating the reducedbillet to about 17 00 F., reducing the reheated reduced billetmaterially, finishing the same at about 1400 F., cold rolling to amaterially reduced thickness, and annealing at not over about 1 150 F.

In testimony whereof, I have hereunto subscribed my name this th day ofDecember,

VERE B. BROWNE.

ing or rolling operation was conducted at a ing a chromium content ofbetween about 10% and about 20%, an aluminum content between about 3%and about 10% with the 340% with the remainder principally iron,

which consists in casting an ingot of such alloy, heating the ingot toabout 2000 F., re-

ducing the same materially by heating and rolling successive steps atprogressively ductile arti-

